This project is aimed at defining stimulus-response relationships involved in the physiological control of LH, FSH, prolactin and TSH secretion in the rat. Part of the program deals with applications of secretory kinetic theory to the analysis of pituitary hormone synthesis and release rates. Analytical methods include: radioimmunoassay and bioassay of stored and circulating pituitary hormones; gross and histological examination of the pituitary and thyroid; tests of thyroid function and measurements of gonadal steroid concentrations in the serum. In vitro studies of the secretory responses of dispersed pituitary cells to synthetic releasing factors and gonadal steroids will be done. A key phase of the program is the use of pituitary grafts for studying the interplay of releasing-factor(s) and steroids in the control of hormone secretion. The findings obtained in these studies of the isolated pituitary, in conjunction with data on the pituitary steroidal milieu in intact rats, will provide a basis for inferences about changes in releasing-factor secretion during spontaneous physiological events.